It is widely believed that Malassezia yeasts, such as Malassezia furfur, are the main cause of dandruff. However, it is unclear why some people suffer from this condition while others do not. What is known is that increasing the level of Malassezia on the scalp does not automatically lead to dandruff. This suggests that Malassezia is necessary but not sufficient to cause the condition.
Recent studies have demonstrated that dandruff is associated with changes in scalp skin condition. Dandruff scalp skin has been shown to have decreased levels of stratum corneum lipids such as ceramides, an increased susceptibility to application of topical histamine and a perturbed balance in the levels of inflammatory cytokine markers in the stratum corneum. These findings clearly demonstrate that dandruff is associated with changes in scalp skin condition and that dandruff is multifactorial. It is believed that the weakened scalp skin barrier and perturbed condition of the scalp skin renders an individual susceptible to challenge by factors such as Malassezia. 
The main, if not only, intervention strategy used on the market currently for the treatment of dandruff is the topical application of antifungals such as zinc pyrithione (ZnPTO), octopirox and ketoconazole which are normally delivered from a shampoo. These antifungal agents remove (or at least reduce the level of) the Malassezia from the scalp, and provide effective treatment of the dandruff condition.
Although clinically proven to be effective in treating the clinical symptoms of dandruff over a two to four week period, there remains a need to treat the main symptoms of dandruff more effectively and rapidly. The main symptoms of dandruff are visible skin flakes in the hair and on the shoulders and scalp itch. Scalp itch is perceived as being a particular problem in certain parts of the world, for example it is the main symptom of dandruff in China, South-East Asia and India.
As well as treating the clinical signs of dandruff, therefore, there remains a need for providing rapid relief from scalp itch for dandruff sufferers.
WO04/00085 describes how cannabinoid receptor (CBR) activators may be useful in hair treatment compositions for the treatment and/or prevention of symptoms of dandruff such as scalp skin itching and flaking.
The present inventors have found that certain amino-oxo-indole-ylidene compounds are capable of acting as CBR activators, and therefore may be used for the treatment and/or prevention of symptoms of dandruff such as scalp skin itching and flaking.
There is no suggestion in WO04/00085 that these compounds would possess such activity. Their structure is unusual compared to known classes of cannabinoid receptor (CBR) activator, as reviewed for example in Howlett et al., Pharmacol. Rev. 54 (2): 161-202, 2002.